In an LTE system, since resources exist in two dimensions, i.e. time and frequency. Accordingly, the allocation of the resources and their representation method become quite complicated, especially when a bandwidth is relatively wide, consideration must be given to such requirements as not only the flexibility of the resources allocation but also the size of the related bandwidth, etc.
FIG. 1 is a schematic illustration of a resource block and a resource element in a 3GPP LTE (with 5M-bandwidth) system. It is specified in the LTE system that the length of a sub-frame in time is 1 ms, and one sub-frame is comprised of two equal time slots (Time Slot 1 and Time Slot 2), the length of time of each time slot is 0.5 ms. One resource element contains one Orthogonal Frequency Division Multiplexing (shortened as OFDM) symbol, and one subcarrier in each OFDM symbol belongs to the resource element. While the usual method of resource representation is defining a basic Resource Block (shortened as RB), and then carrying out the resources allocation in the unit of RB.
In the LTE system, a downlink mainly includes multiple downlink channels such as a Physical Control Format Indicator Channel (shortened as PCFICH), etc. A representation method for mapping a physical downlink control format indicator channel to physical resources is given in a current draft standard, which is specifically described as below:
mapping y(0), . . . y(3) to the resource elements in which a resource element group k locates, and k=k0;
mapping y(4), . . . y(7) to the resource elements in which a resource element group k locates, and k=k0+└NRBDL/4┘;
mapping y(8), . . . y(11) to the resource elements in which a resource element group k locates, and k=k0+└2NRBDL/4┘;
mapping y(12), . . . y(15) to the resource elements in which a resource element group k locates, and k=k0+└3NRBDL/4┘;
wherein, k0=NIDcell mod(NRBDL/2, and it is necessary to carry out a modulus of NRBDLNscRB on k;
wherein, y(0), . . . , y(15) stand for the data in the physical downlink control format indicator channel after code modulation, and the NRBDL stands for the quantity of resource blocks in the system bandwidth, and the NIDcell is the proprietary ID (identity) of each cell.
Taking the 3GPP LTE (with 5M-bandwidth) system for example, as shown in FIG. 1, a 5M-bandwidth downlink in the LTE contains a total of 512 subcarriers, the 300 of which in the middle are usable subcarriers; each resource block contains continuous 12 subcarriers, therefore the 5M bandwidth contains a total of 25 resource blocks.
One resource block contains 4 pilot elements, and except the pilots, every four remaining resources elements are combined into a resource element group, so there are a total of 50 resource element groups.
The physical downlink control format indicator channel is mapped to the first OFDM symbol in a sub-frame.
Assuming that the ID of the target cell is 13 and that the initial position of the pilot on the first antenna port is the third subcarrier, then:
according to the existing technologies, and k0=NIDcell mod(NRBDL/2); when the NRBDL is an odd number, the k0 would be a decimal number, which does not offer any practical physical meaning; and
moreover, even if k0=NIDcell mod(└NRBDL/2┘) or k0=NIDcell mod(┌NRBDL/2┐), there is still a problem that the performance is not optimal.
y(0), . . . y(15) in the physical downlink control format indicator channel are mapped to the following physical resources by dividing 4 continuous subcarriers in order except the pilots into one group:
wherein, y(0), . . . , y(15) stand for the data in the physical downlink control format indicator channel after code modulation; the NRBDL stands for the quantity of the resource blocks in the system bandwidth; and the NIDcell is the proprietary ID of each cell.
k0=NIDcell mod(NRBDL/2)=13 mod(└25/2┘)=1, and it is necessary to carry out a modulus of NRBDL×NscRB=25×12=300 on k;
y(0), . . . y(3) are mapped to the resource elements in which a resource element group k locates, and k=k0=1;
y(4), . . . y(7) are mapped to the resource elements in which the resource element group k locates, and k=k0+└NRBDL/4┘=1└25/4┘=7;
y(8), . . . y(11) are mapped to the resource elements in which the resource element group k locates, and k=k0+└2×NRBDL/4┘=1+└2×NRBDL/4┘=13; and
y(12), . . . y(15) are mapped to the resource elements in which the resource element group k locates, and k=k0+└3×NRBDL/4 ┘=1+└3×25/4┘=19.
FIG. 2 is a schematic illustration of mapping a physical downlink control format indicator channel in a 3GPP LTE (with 5M-bandwidth) system according to relevant technologies. As shown in FIG. 2, the code-modulated data y(0), . . . , y(15) in the downlink control format indicator channel are mapped to the resource elements numbered 6, 7, 9, 10 and 42, 43, 45, 46 as well as 78, 79, 81, 82 and 114, 115, 117, 118.
It can be seen in FIG. 2 that the range of physical elements which are mapped to a physical downlink control format indicator channel by the existing solution is only half of the bandwidth, without obtaining a maximum gain of frequency selectivity.
In the LTE system, the resources in the physical downlink control format indicator channel are allocated based on 4 continuous subcarriers as a group, while in the system bandwidth and except the pilots, the resources are divided into groups of 4 continuous subcarriers (the pilots are skipped over if they are encountered), so the total number of the groups is 2NRBDL (because one RB contains 12 carriers, while one RB also contains 4 subcarriers used for dual-antenna pilots). And there are 16 modulated data in the physical downlink control format indicator channel which need to be mapped onto 4 groups (each group has 4 subcarriers). If mapping should be carried out according to the formula in the above mentioned draft standard, then the data in the physical downlink control format indicator channel would be distributed unevenly over the entire system bandwidth, and thereby that is unable to obtain the maximum gain of frequency diversity.